Her Republican opponent, businessman David Perdue, also is running as the “change” candidate, but he’s skipping the collaborative stuff. He says he’ll go to Washington to attack President Barack Obama and Democratic Senate leader Harry Reid.

How this argument plays out matters. An upset by Nunn in Georgia, which has been solidly Republican for more than a decade, was long considered just a bonus possibility for her party. Now Democrats have six or seven very vulnerable Senate seats in the Nov. 4 elections, and a loss of six would cost them the majority. The party needs to win in a couple of Republican-held states. Georgia, where the incumbent Republican senator, Saxby Chambliss, is retiring, is one of the two best options for a Democratic victory.

Democrats hoped to run against one of Georgia’s House incumbents. Instead, they face a political newcomer, a corporate executive and cousin of former governor Sonny Perdue.

This race is surprisingly close because of the state’s changing demographics. As recently as 2004, whites, who vote overwhelmingly Republican, accounted for 71 percent of the electorate. In 2012, they comprised a little more than 61 percent. The black vote, almost all Democratic, grew to 30 percent from less than 25 percent, and the small Hispanic vote is increasing. The Atlas Project, a Democratic organization that studies voting patterns, projects that this trend will continue.

There has been speculation that Texas, with its fast-growing Hispanic population, could turn from a reliably Republican state to a battleground or purple one. That’s likely to happen in Georgia first.

Democrats say they’re competitive in Georgia this year because of two candidates with impressive political pedigrees. Nunn is the daughter of a much-admired former senator, Sam Nunn. The Democratic gubernatorial aspirant is Jason Carter, the grandson of former president Jimmy Carter.

This year “is a gift,” says Stacy Abrams, the Democratic leader in the Georgia House of Representatives who spearheaded the registration of 120,000 new voters and will lead the turnout drive. “The demographics are not yet sufficient, but we have two strong candidates with strong names.”

The math is simple. Nunn needs close to 30 percent of the white vote — Obama got about 23 percent in Georgia in 2012 — and she needs a turnout of black voters only slightly smaller than the 30 percent level blacks represented in the 2012 presidential election. Perdue needs to get 75 percent of the white vote to at least match the share of the total electorate whites represented two years ago.

He’s running against Washington, the president and the immigration-reform bill, which he calls amnesty. He also wants to repeal the Affordable Care Act.

Nunn has a tougher tightrope to walk: She needs to appeal to the base by embracing pay equity for women, a higher minimum wage, immigration reform, and mend, not end, the Affordable Care Act. Simultaneously, she has taken as a model her father’s record as a fiscal moderate and national-security realist, promising to “reach across the aisle” to seek bipartisan accords.

She has impressive business supporters, such as Mitesh Shah, the chief executive officer of a private-equity real estate firm. A lifelong Republican, Shah says he is bothered by his party’s rightward drift on social issues such as immigration.

“I may not always agree with her, but I think Michelle is different and can make a difference in Washington,” Shah said.

Three debates will make a difference. The first, on Tuesday, will probably include a mention of Nunn’s role as the head of former President George H.W. Bush’s Points of Light foundation. Last month, Bush endorsed Perdue. Later, the Republican campaign broadcast an ad that accused Nunn of favoring amnesty for undocumented immigrants and suggested Points of Light funded organizations linked to terrorists.

Independent analysts have dismissed the charge as bogus. Nunn, sensing that the ad has backfired, pounced on it.

“This is what people are so tired of in politics,” she said in an interview. Perdue, in an interview, defended the ads. “This is about national security and border security,” he said.

Perdue has run as a job creator. On Friday, however, a nine-year-old deposition came to light in which he readily acknowledged that as a chief executive he had outsourced jobs.

Polls show a tight race, which includes a libertarian candidate expected to get 3 to 4 percent of the vote. If no candidate gets 50 percent, Georgia law requires a runoff on Jan. 6.

Both camps agree that would be a nightmare, especially if control of the Senate is at stake. Experts predict that $100 million in campaign funds would pour into Georgia during the two-month runoff.